In recent years, display devices using organic electroluminescence (EL) elements have vigorously been developed, which have features of self-emission, a high response speed, a wide viewing angle and a high contrast, and which can realize small thickness and light weight.
Patent document 1 (Jpn. Pat. Appln. KOKAI Publication No. 2008-270731), for instance, discloses an organic EL element including a buffer layer, which is composed of a multilayer structure of inorganic materials with hole transportability and electron-blocking properties, between a pixel electrode and an organic light emission layer. In particular, this patent document 1 discloses, as the buffer layer, a multilayer structure comprising a hole transport layer and a functional layer, which are formed of, e.g. an oxide, a nitride, or an oxynitride of a transition metal.